Unusual steel joist - Civil Engineering - Engineer Boards
Jump to content
Engineer Boards
Sign in to follow this  
ChaosMuppetPE

Unusual steel joist

Recommended Posts

I've ran across a manufactured joist that I've never seen before and it has me slightly confused.

I've tried to back out an allowable loading using both A7 and A36 steel as this transition occurred while poured gypcrete roofing was being used, however, neither steel designation gives me anything close to what I anticipate the design loading should be. I've checked and double checked the section properties and the chord shapes appear to be formed from one piece. I've incorporated a sketch for reference.

If you've seen anything like this before, please tell me what you can about it. Preferably, I'd like to know the manufacturer of joists of this type. I suspect the structure was built in the early 60's in the Atlanta area.

 

 

UNUSUAL JOIST.jpgSKETCH UJ.jpg

Share this post


Link to post
Share on other sites

Not sure if you've solved this yet but looks like it could be a Macomber joist? There's some old catalogs/info on them on this site: http://www.slideruleera.net/contributions.html

  • Like 1

Share this post


Link to post
Share on other sites
On 8/16/2019 at 12:32 PM, ThrustIssues said:

Not sure if you've solved this yet but looks like it could be a Macomber joist? There's some old catalogs/info on them on this site: http://www.slideruleera.net/contributions.html

agree it looks like a macomber!

Share this post


Link to post
Share on other sites
On 8/16/2019 at 3:32 PM, ThrustIssues said:

Not sure if you've solved this yet but looks like it could be a Macomber joist? There's some old catalogs/info on them on this site: http://www.slideruleera.net/contributions.html

@tj_PE

I appreciate the input. I did eventually find Macomber and it does "favor" one, but it appears to be a competitor as the profile I have doesn't match anything in their manual.

It's just one of those situations where I'm stuck. I've calculated all the section properties for the joists and backed out the loading from this. The closest section to my joists in the Macomber manual gives an allowable loading of roughly 134plf and the joist I have back calculated to 140plf so I have a feeling I at least have the material designation right. The issue I have is that dead load alone is almost this high. It appears these joists were actually only designed for dead load unless there is some kind of composite action I am not aware of with the gypsum tees. Either way, it's the first time I've encountered this.

Edited by ChaosMuppetPE
I'm mentally slow.

Share this post


Link to post
Share on other sites

I can write everything I know about structural engineering on the back of a postcard - with lots of space left over -  so I'm ignorant but curious. Wouldn't it be a bit reckless to design something only for the dead load? Surely the environmental and live loads can't be neglected?

Share this post


Link to post
Share on other sites
46 minutes ago, RBHeadge PE said:

I can write everything I know about structural engineering on the back of a postcard - with lots of space left over -  so I'm ignorant but curious. Wouldn't it be a bit reckless to design something only for the dead load? Surely the environmental and live loads can't be neglected?

yeah, that's why chaos is perplexed. it's an existing building so likely trying to analyze what the original capacity was so he can check it for new use/loads etc. 

@ChaosMuppetPE I feel like maybe it was considered composite, otherwise why would they put concrete on the roof? is there deck under it or just a structural slab? 

are there spiders? maybe just burn it down? 

  • Like 1
  • Thanks 1

Share this post


Link to post
Share on other sites

@tj_PE Are we calling gyp deck concrete these days?  😐

@ChaosMuppetPE 

Note: I have a deep dislike of gypsum as a roofing material, particularly in the cold, wet, midwest where snow sits and seeps through any holes in the the roofing material.  I'm sure it could be an acceptable material if it is kept dry and in pristine conditions, otherwise might as well put mashed potatoes on the roof.  

 

Share this post


Link to post
Share on other sites
4 minutes ago, vhab49_PE said:

@tj_PE Are we calling gyp deck concrete these days?  😐

 

my sincerest apologies; gypcrete*

Share this post


Link to post
Share on other sites
Just now, tj_PE said:

my sincerest apologies; gypcrete*

I really, really hate it.  

Share this post


Link to post
Share on other sites
Just now, vhab49_PE said:

I really, really hate it.  

I've never had it used in new buildings, so that's a plus. 

we use it for topping slabs sometimes, but it is very often swapped in/out with "real" concrete topping 

Share this post


Link to post
Share on other sites
4 minutes ago, tj_PE said:

I've never had it used in new buildings, so that's a plus. 

we use it for topping slabs sometimes, but it is very often swapped in/out with "real" concrete topping 

I have 4 projects right now that are renos of old buildings that have gyp roof.   ugh.  

  • fudgey 1

Share this post


Link to post
Share on other sites
2 hours ago, tj_PE said:

yeah, that's why chaos is perplexed. it's an existing building so likely trying to analyze what the original capacity was so he can check it for new use/loads etc. 

@ChaosMuppetPE I feel like maybe it was considered composite, otherwise why would they put concrete on the roof? is there deck under it or just a structural slab? 

are there spiders? maybe just burn it down? 

I definitely like the spiders/burn it down idea. Design it for whatever, get paid, and light a fire. No liability/no problem.

  • Like 1
  • Haha 1

Share this post


Link to post
Share on other sites

@vhab49_PE@tj_PE

I'm sure it has to be composite. It's the only feasible explanation. I mean, I am retarded, but I am able to calculate section properties. Without doing destructive demo, I don't have  a solution for anticipating the gypcrete compressive strength, the tee attachments, or even the tee size. I am just going to reinforce the bajeebus out of it with steel bar stock or require the owner to perform destructive testing. For (10) 50' span joists, I'm not sure what would be cheaper.

Share this post


Link to post
Share on other sites
Just now, ChaosMuppetPE said:

@vhab49_PE@tj_PE

I'm sure it has to be composite. It's the only feasible explanation. I mean, I am retarded, but I am able to calculate section properties. Without doing destructive demo, I don't have  a solution for anticipating the gypcrete compressive strength, the tee attachments, or even the tee size. I am just going to reinforce the bajeebus out of it with steel bar stock or require the owner to perform destructive testing. For (10) 50' span joists, I'm not sure what would be cheaper.

is there any option to just sister joists in there? if you're reinforcing the joists piece by piece maybe it's more cost effective. would be a bitch to get them in the building and put up there but maybe you can splice them somewhere or if the shear capacity is OK on existing you could just put a new one in for the bending critical and connect to existing somehow? actually maybe just easier to reinforce.

or a channel? steel plate?  just thinking hypothetically. I haven't done much joist reinforcement so not sure how much labor work is involved. 

Share this post


Link to post
Share on other sites
On 8/3/2019 at 9:28 AM, ChaosMuppetPE said:

I've ran across a manufactured joist that I've never seen before and it has me slightly confused.

I've tried to back out an allowable loading using both A7 and A36 steel as this transition occurred while poured gypcrete roofing was being used, however, neither steel designation gives me anything close to what I anticipate the design loading should be. I've checked and double checked the section properties and the chord shapes appear to be formed from one piece. I've incorporated a sketch for reference.

If you've seen anything like this before, please tell me what you can about it. Preferably, I'd like to know the manufacturer of joists of this type. I suspect the structure was built in the early 60's in the Atlanta area.

 

 

UNUSUAL JOIST.jpgSKETCH UJ.jpg

Did you consider AISI 1018 or AISI 1020? Both were pretty common in those days from what I can gather.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
Sign in to follow this  

×
×
  • Create New...